Battle Borers Without Bt

If you want to save a few dollars on seed, but also want some corn borer protection, give naturally tolerant hybrids a shot.

"These hybrids, which are somewhere between conventional and Bt hybrids, provide good early protection against European corn borers," says Mike Mueller, a regional agronomist in northern Illinois and northern Indiana for Mycogen Seeds. "They provide resistance until about the 12th-leaf stage and provide tolerance thereafter."

Mueller points out that corn borer larvae feed on these hybrids, but the plant isn't palatable. Therefore, they eat more slowly than on conventional hybrids and do less damage.

"In years when there is corn borer pressure, a farmer would need to spray conventional hybrids to get standability and yield protection," Mueller notes. "He saves that cost by planting native-tolerant corn."

The native tolerance can be bred into a hybrid, just as any other agronomic trait is bred in, Mueller says.

Many seed companies now evaluate their hybrids for natural tolerance to corn borers. For example, Golden Harvest, in its 1999 lineup of hybrids, had several that it described as having good or excellent natural tolerance to first-generation borers. It also listed a few hybrids with good natural tolerance to the first and second generations.

"Besides the non-palatable factor, part of the tolerance can come from a tougher rind," says Lee. "With some naturally tolerant hybrids, corn borers can't penetrate the rind. And with some hybrids they can penetrate the rind but the hybrids still yield well. Those hybrids have a natural resistance to fungi and therefore little or no disease enters the stalks."

He reports that it's difficult to breed a hybrid with both high yield and natural borer tolerance. But a few hybrids have both traits.

"Farmers who are in high-risk areas for corn borers, or who have high-yielding soils and have a moderate to high risk of corn borers, probably should plant Bt hybrids," Lee recommends. "Farmers who are in a low-risk area for corn borers, or who are in an area where yields are uncertain, may want to consider hybrids with natural tolerance to corn borers."

He suggests that hybrids with natural tolerance be planted in Bt refuge areas. "That tends to maximize total yields," says Lee.

Jim Schmitt, who farms with his brother Norman near Tonica, IL, began planting Mycogen's 7250, a tolerant hybrid, in 1993. That was before Bt hybrids were available.

"It yielded 240 bu/acre in a plot that first year, and that was 30 bu better than anything else," Schmitt reports. "We can expect heavy corn borer pressure five years out of 10 in this area," Schmitt says. "So these days we plant 75% Bt corn and much of the rest, which is our refuge area, in 7250."

Professional farm manager Kent Smith and his colleagues at Stalcup Ag Service, Storm Lake, IA, increased their use of hybrids with natural tolerance in 1999.

"We have screened the performance of corn hybrids very closely," says Smith. "We have found that certain hybrids have good natural tolerance to corn borers and also are top yielders. Plus, they don't have a tech fee."

Smith had nearly 50% Bt hybrids on farms he managed in 1998. Last year he cut back to about one-third Bt and replaced those areas with naturally tolerant hybrids. ?